#include<stdio.h>
int main(int argc, const char *argv[]){
	int num=0,res=1;
	if(argc!=2||sscanf(argv[1],"%i",&num)==0||num<=0){
		fprintf(stderr,"usage: %s [positive-integer]",argv[0]);
		return 1;
	}
	while(num>0){
		res*=(num--);
	}
	printf("%d\n",res);
	return 0;
}
